1. Field of the Invention
The present invention relates to a method, system, and program for maintaining and using nexus information on a host, port and device connection
2. Description of the Related Art
In certain computing environments, multiple host systems may communicate with one or more storage controllers, such as an IBM Enterprise Storage Server (ESS)®, for data in a storage device managed by the ESS receiving the request. The storage controller manages access to storage devices, such as interconnected hard disk drives through one or more logical paths. (IBM and ESS are registered trademarks of IBM). The interconnected drives may be configured as a Direct Access Storage Device (DASD), Redundant Array of Independent Disks (RAID), Just a Bunch of Disks (JBOD), etc. The storage controller may configure logical volumes that define regions of storage space in the storage devices the storage controller manages.
The storage controller or an adaptor in the storage controller may maintain nexus information on each possible connection comprising a host port, storage controller port, and storage device (logical volume). In the Small Computer System Interface (SCSI), an initiator (I) interacts with a target(T) to issue I/O operations to a logical unit (L). While the I/O operation is in progress, the initiator/target/logical unit have a relationship referred to as an ITL nexus. In order to manage an ITL nexus, a storage controller may need to maintain certain information that persists beyond the duration of the I/O operation. For instance, this information may consist of indicators related to pending unit attention conditions and reservations. In a typical implementation, the initiator function is associated with a host port, the target function is associated with a storage controller port, and the logical unit is associated with a storage device. This information is maintained even for host port-storage controller port-logical volume combinations that do not currently have configured logical volumes since they may be added to the configuration at a later time. The memory needed to store the nexus information increases as the number of devices, storage controller ports, and attached host-ports in the configuration increases.